A category USAAC was lagging behind RAF LW for a better part of the war.
How would've looked a good night fighter plane if you were in charge of development production? Assuming starting date is June 1st 1941, using as much off-the-shelf stuff as possible, while encouraging to look beyond licence-produced Mossie
A decent-sized force in combat units by March 1st 1943 is the objective.

My 1st take would be the twin hull P-40.
Radar set like one from contemporay Beaufighter, up to 6 .50 cals in central wing, outer wings sporting fuel tanks instead of MGs ammo. Packard Merlins, if possible.
I'll post the picture later.

The Mosquito night fighter entered service during January 1942. Some aircraft were produced in next door Canada. No need to look further. Just place an order for enough Mosquito night fighters to meet American requirements.

If necessary the Canadian factory would be expanded with American money. Just like General Motors establishing subsidiary automobile factories in next door Canada. 8)

How about a TBF Avenger based night fighter?
It has decent range/endurance.
May have room necessary for radar and such.
I imagine the airframe could have accommodated the changes necessary for the application.

Avenger with less weight more power (R-2800 'stead of R-2600, but the weight goes up then)? Perhaps enough performance to hit unwary Japanese night bombers?
IIRC Avenger was mentioned as a makeshift night-fighter in one of the episodes of 'Dogfights' @ History chanel.

How about 2-seater F6F, F4U, or P-47? Radar aerials either at wings, and/or behind the prop, like the Defiant.

two seat conversions of these planes need a lot of rework. Second seat it pretty much going to go where the fuel tank is. Navy pretty much had the Night fighter thing covered with the single seat versions anyway.

If the P-70 with two R-2600s wasn't fast enough (or had enough climb/altitude performance) why would the Avenger with one R-2600 be a success?
Lots of planes were pressed into the night fighter role, doesn't mean they were much good at it.

Edit. Navy (marine) PV-1's were also used as night fighters. Not much for ceiling but they were pretty fast for a plane their size. Perhaps not much use in Europe.

two seat conversions of these planes need a lot of rework. Second seat it pretty much going to go where the fuel tank is. Navy pretty much had the Night fighter thing covered with the single seat versions anyway.

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P-47 has space between pilot's seat intercooler, occupied by radio in real P-47s. Enough of space for a radar operator some of it's gear. We need to relocate oxygen tanks into wing leading edges, and radio itself in aft hull.
Or a shape of Curtis-built P-47 'Doublebolt', with extra fuel tankage behind (now) second seat, to 'return' the fuel lost by cuting the main fuel tank.
F6F has plenty of space behind pilot, so not too much trouble here.
As for F4U, the solution might come by elevating crew compartment; main fuel tank loses 1/3rd of it's capacity, since the pilot would've been relocated somewhat forward, too. The radar operator can be located slightly aft of the original pilot+s place. Since we've elevated crew compartment, new fuel tank can be located under crew, not unlike F4F sported it's main fuel tank.

I'm with Shortround on this bit of hyperbole. Pushing development of the North American P-61 would have been the most far-sighted move. The Lockheed Ventura, many of which were in production on a French order and later Lend-Leased to the Brits, might have provided an interum solution. Regards

Once again, just because there is space/volume in part of an aircraft doesn't mean you can stuff it with what ever you want. Fuel tank behind cockpits of the doublebolt really screws up the CG situation.
Early F6F/F4U night fighters had antennae in the pod but much of the electronics was in the radio bay behind the seat.

Planes with half of the weight of P-47 have had fuel tanks aft of CoG. Benefits outweighed shortcomings.

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Not all planes react to CG shifts the same. What benefit is there? a P-47 night fighter that is more crash prone than a regular P-47 vs a proper night fighter or interim one like the P-70 or PV-1?

Loosing more trained crews in operational accidents might not be considered a "benefit" by the operational staff let alone the crews themselves.

Historically the US "borrowed" Beaufighters to Equip it's first European/Mediterranean/NA night fighter squadrons. Jumping though hoops to come up with dangerous to fly night fighters just so that they will be "ALL AMERICAN" just a few months before the P-61s begin to show up seems rather pointless.